Pumping apparatus with electromagnetically propelled piston



Feb. 1', 1955 J. c. HOLST 2,701,331 PUMPING APPARATUS WITH ELECTROMAGNETICALLY PROPELLED PISTON Filed Aug. 29, 1949 3 Sheets-Sheet l 34 Fig.

Inventor John 6. Holst Feb. 1, 1955 J. c. HOLST 2,701,331

PUMPING APPARATUS WITH ELECTROMAGNETICALLY PROPELLED PISTON Filed Aug. 29, 1949 5 Sheets-Sheet 2 30 r 1, I56 I54 Fig.2.

John C. Ho/sl 56 IN VEN TOR.

(Wavy yM Feb. 1, 1955 J. c. HOLST 2,701,331

PUMPING APPARATUS WITH ELECTROMAGNETICALLY PROPELLED PISTON Filed Aug. 29, 1949 3 Sheets-Sheet 3 I04 Fig. 3.

Fig.5.

John C. Holst IN VEN TOR.

United States Patent PUMPING APPARATUS WITH ELECTROMAGNETI- CALLY PROPELLED PISTON John C. Holst, Salt Lake City, Utah, assignor of one-third to Lynn W. Bennie, Dallas, Tex., and one-third to Frank K. Bennie, Trona, Calif.

Application August 29, 1949, Serial No. 112,911

5 Claims. (Cl. 318-128) This invention relates to pumping apparatus in which the piston is driven electromagnetically by solenoid coils surrounding the pumping cylinder and it has for its main object to improve the elficiency of the electromagnetic driving means and of the control mechanism of said driving means.

Electromagnetically driven pumps have mostly been used for extremely small pumping mechanism or for pumps delivering extremely small quantities of liquid in which the efiiciency of a mechanically driven pump is very poor so that the electromagnetic driving means, notwithstanding their inherent lack of efiiciency, can favorably compare with the mechanical drive. However, the electromagnetic driving means has an efliciency which is far below that of the mechanical driving means in all those cases in which the size of the pump or the quantity delivered by the pump is not extremely small.

Pumps of the electromagnetically propelled type also have the disadvantage that the reciprocating movement of their piston lacks smoothness and uniformity when compared to pistons which are mechanically driven so that the cylinders and pistons are subjected to shocks and concussions. A further disadvantage consists in the fact that the adjustment of the propelling force is ditficult to perform. Moreover the methods used for the control of the propelling magnetic fields are extremely disadvantageous and cause rapid acceleration near the point where a change of direction occurs without any previous deceleration of the moving masses, thus producing undesirable losses, noisy operation and the development of heat.

It is therefore an object of the invention to provide an electromagnetic pumping apparatus with a piston propelled by the electromagnetic force of solenoid coils in which the electric input energy can be utilized to a higher degree of efficiency than in the pumps of this type hitherto known.

It is a further object of the invention to eliminate the mechanical control of the contact switch or contact members controlling the operation of the propelling solenoids and the production and the reversal of the electromagnetic propelling field so that the pump cylinder may form part of a completely closed system without seals around moving parts projecting from the cylinder and reaching the outside.

It is a further object of the invention to replace the mechanical control methods for the control of the energization and reversal of the electromagnetic fields propelling the piston by methods producing energization and reversal of the direction of the propelling forces at points at which a deceleration may precede the actual reversal of movement of the moving parts, thus producing a more balanced operation and reducing or eliminating the shocks and concussions due to sudden and belated reversals.

It is a further object of the invention to use control methods allowing a fine adjustment of the point at which reversal of direction of the propelling force for the piston may take place. It is a further object of the invention to provide a method for controlling the electromagnetic propelling force which permits an action of the piston on the contacts or other current distribution members which is based on electromagnetic action and which may therefore be exercised at a distance without physical contact of the piston with other members.

A further and more specific object of the invention 2,101,331 Patented Feb. 1, 1955 consists in using inductive means, influenced by the piston which are so arranged on both sides of the pump cylinder that one of them is influenced by the piston to a higher degree than the other when the piston nears one of its end positions, the difference between the two inductive influences producing an operation of the control switich controlling the energization of the propelling solenoi s.

A further specific object of the invention consists in using reactance coils which are coaxial with the cylinder and which are directly influenced by the entry of the piston into the space intersected by the field of said coils, the current fluctuations, thus produced being used to operate the control switch.

Further objects of the invention are of a more specific character and will be described in the following detailed specification.

The invention is illustrated in the accompanying drawings showing several modifications and embodiments of the same. It is, however, to be understood that the specific embodiments which have been selected in order to illustrate the invention are shown by way of example in order to illustrate the principle on which the invention is based and the best mode of applying said principle. Modifications of the embodiments of the invention illustrated in the drawings are therefore not necessarily departures from the principle of the invention.

In the accompanying drawings:

Figure 1 is a diagrammatic view of one embodiment of the invention, the cylinder being represented in section.

Figure 2 is a similar diagrammatic view of a modification of the invention as shown in Figure 1.

Figure 3 is a diagrammatic sectional and elevational view of a further modification of the invention, the diagram also showing the connections used.

Figures 4 and 5 are diagrammatic sectional views of further modifications of the invention, both modifications using a tiltable switch operated by a rockable armature.

Figure 6 is a diagram of a further modification of the invention.

Figure 7 is a cross sectional View of a detail.

In order to understand the invention more fully it may first be explained that pumps for fluids which should not come into contact with the air or with air under pressure or should not be subjected to temperature conditions prevailing outside the pump are most diflicult to construct and to operate because all mechanically driven pumps must be provided with a power transmitting rod, shaft or other member projecting outwardly. These rods, shafts or other members have to be sealed but it is diflicult to obtain a completely tight seal of an outwardly projecting rod, shaft or other member without friction and consequent abrasion which destroys and impairs the seal within a relatively short time. However, if the seal is obtained without friction or with a slight friction only it is unavoidable that small quantities of the fluid or liquid penetrate to the outside where they may cause damage or where they may interfere with the operation of the pump for instance by freezing or by becoming sticky.

In order to avoid these difiiculties pumps with electromagnetically propelled pistons may be used which may be driven within a completely closed cylinder forming part of a completely closed system. However, pumps with electromagnetically propelled pistons, such as hereto known, do not fulfill the above mentioned requirement as they use control members, operated by the piston and controlling contacts outside the cylinders some of which have to pierce the cylinder and which therefore have to be sealed. Moreover, the hitherto known pumps with electromaguetically propelled pistons have many disadvantages, such as a rather poor efficiency and they are therefore rarely used commercially, except in the case which has been mentioned before.

Among the disadvantages preventing such commercial use, are those connected with the means for controlling the distribution of current. In order to obtain a reversal of the piston at the precise moment at which the piston has arrived at the end of its stroke the energization of the propelling solenoids must be so controlled that the propelling power in one direction is cut out at the moment at which the propelling power in the opposite direction becomes operative. A smooth operation of the piston can however not be obtained, if controlling contacts mechanically operated by the piston at the end of the stroke are-used as the latter is kept moving at full forceuntil the reversing-contact is touched, whereupon immediate reversal occurs, the propelling force now acting on the piston in the opposite direction. Shocks and-concussions are therefore unavoidable.

Another major disadvantage consists in the pooreffi ciency of the transmission of the propelling force to the piston, the energy supplied to the propelling solenoids be ing usually a multiple of the energy .with which'fluid is driven out by the piston.

Itis therefore necessary inorder tomakesuch pumps usable to avoid the above named major defectsofthe knownconstructions and, according to'the inventioruan improved transmission of power with high .eflic-iencytakes place while simultaneously an improved switch, controlled without any mechanical connection with the .piston, is introduced.

In the modification illustrated in Figure 1 merely an improved control mechanism is shown. The reciprocating piston 12 of ferromagnetic material is arranged and moved within a cylinder .10, made of brass, non-magnetic steel or of any other non-magnetic material. The cylinder is surrounded by the piston propelling solenoid coils 14, 16 which are coaxial with the cylinder, each coil covering approximately one-half of the length of the cylinder. The coils are however slightly shorter than the piston which may have a length corresponding to one-half of the cylinder length. Therefore, the piston always projects somewhat from the coil even when in its end position.

The cylinder is closed at both ends by means of lids 18, 20, each of which contains merely the opening into which the pipe 24 for supplying and delivering fluid is screwed. The supply and delivery of fluid to the pump through pipes 26, 28 is regulated by the valves 30, 32 which are of the usual type and which therefore need not be described.

The piston propelling solenoid coils 14 and 16 may be encased within a non-conducting holder or container 34. Alternatively the coils may simply be provided with .a coating consisting of plastic materiahas usual.

Each coil has the required number of turns for producing a strong magnetic field in its interior into which the piston 12 is drawn upon energization of the coil with the force which is necessary in order to deliver the fluid at the required pressure.

Each of the piston propelling solenoid coils 14, 16 forms part of a circuit 36, 38 respectively, which circuits may have a common branch 40 leading to a source .of direct current 42. Each circuit is controlled by one of the reversal control contacts 46, 48 of a propulsion control switch which cooperate with and are alternately contacted by a movable switch or contact arm 50, connected with the common branch 44 of the two circuits leading ,to the source of direct current supply 42.

The movable contact is preferably rockable around the pivot point 52 and is moved by the control relays which, in the example illustrated in Figure 1, are shown as solenoids 54, 56 energized by circuits 58, 62 respectively, and provided with movable cores which are partly ferro-magnet'ic and partly magnetically non-permeable. These movable cores are indicated at 54a and 56a respectively, The circuits 58, 62 are connected with coils 60, 66.preferably provided with laminated cores which may be aligned with the cylinder axis and which are located in immediate proximity to the cylinder lids 18, 20.

it will be understood that the solenoids 54, 56 may have the form of the customary relays or electromagnets acting on an armature formed by the movable arm 50. This action may be an electromagnetic action of the relays on the armature instead of the mechanical action which has been shown in the figures and which is exercised by the cores 54a, 56a the ferro-magnetic portion of which is drawn into the interior of the coils 54, 56.

The circuits 58, 58a and 62, 62a join at 64 and are connected with a source of current 68 which is preferably a source of A. C. Likewise the relay coils 54, 56 are joined by means of conductors 72, 74 to a common conductor 70 which is connected with the other terminal of the source of current 68.

The arrangement as shown in Figure 1 illustrates one method of control of the propelling solenoid coils. The methodas illustrated, permits the use of D. C. as'a source of current 42 for operating the piston propelling solenoids 14, 16 while A. C. is used as a source for the control relays or solenoids 54, 56 which must be constructed for such operation. It will be noted that the energizing circuit for the propelling solenoid coils is completely separate from he con rol circui The D. C. used for energizin the last mentioned circuit may of course be produced by rectification, if necessary. The use of D. C. for the propelling solenoid coils is preferable to the use of A. C. on account of the higher efiiciency with which the coils operate in the case of a D. C.

The operation of the pump system is based on the alternative energization of the piston propelling solenoids 14, 16. When the piston is moved towards the right in Figure 1, for instance, the magnetic field in the interior of the propelling solenoid is concentrated axially when the piston enters the solenoid coil and reaches maximum concentration when the piston arrives at the end of the cylinder thus filling the interior of the coil. This concen: trated field which is also channeled in a predetermined direction acts on the coils 60, .66. it may be further channeled by the cores of the said coils. This fieldnow may act inductively, as for instance shown in Figure 3 and as will be explained later, or the field mayproduce a change of the reactance in the circuits 58,5,8a or 62, 624 respectively. Whether the reactance upon approach of the pistonincreases or decreases depends on the winding of the coils, onthe use of an iron core and on its mag! netization. However, a change of reactance inthe two circuits ,58, 62 respectively will always be a change in the opposite sense. For instance let it be assumed that the solenoids 54 and 56 move their cores 54a and 56a in, wardly upon energization, and let it further be assumed that the reactance in cir uit 2, 62a increases and the reactancc in cir 8, 5 cr as s e h Pi ton moves to the right in Figure 1; then, upon such move? ment of the piston the increase of the reactance in circuit 62, 62a causes the relay 56 to hold" the core. 56a with less power. Therefore the attraction between core 54a and coil 54 overcomes the corresponding forces whichare active between the core 56a and coil 56 and the arm of the propulsion control switch is shifted to the right, thus cutting out the propelling solenoid 14 and switching in the solenoid 16. The piston therefore returns towards the left in Figure 1.

Manifestly the adjustment of the action of the piston on the relays or solenoids 54, 56 may be relatively very finely adjustable and suitable means (not shown) may be used in order to vary such adjustment. Moreoventhe counter-electromotive force which is produced in coil 66 by the piston 12 advancing toward said coil acts as a braking force so that the piston is not at full speed when arriving in its end position. This braking action of th coil 66 will also remain active after the solenoid 14 has been cut out.

The operation of the pump is therefore rendered much smoother and it resembles more nearly the operation in the case of a positively driven pump connected with a prime mover, as the piston, when arriving at the end of the cylinder has previously been .decelerated.

In Figure 2 a modification of the arrangement shown in Figure 1 is illustrated in which the two coils and 66 are replaced by small identical transformers 80, 81 which may or may not be provided with an iron core. Each transformer comprises a primary coil 75, 77 respectively, cooperating with a secondary coil 76, 78 respectively, Theprimary coils are connected with a source of current 68 and may be connected in series or in parallel. Each secondary'transformer coil 76, 78 is directly connected by means of circuits 79, 80a with the two relays or solenoids 54, 56 respectively. In all other respects the arrangement shown in Figure 2 is identical with the one just described.

The op ra ion of this arrangementd-itfers onlyinsc'far From the one abo e des ri s th position. of the piston 12 .Within the cylinder may assist by its influence orrthe coupling of the primary and of the secondary of the transformers 80, 81 the operation abovedescribed.

When the piston is at rest in the middle of the cylinder the two secondary transformer coils 76, 78 are obviously energized in the same way as their couplings with'the primary and with their loads coils formed by the solenoids 54, 56 are identical. When the piston however is moved towards the right in Figure 2, in addition to the change of inductance in coil '77 the magnetic field concentrated by the piston and passing through the transformer 81 reinforces the coupling between the coils 77 and 78 thereby causing an energizing of the solenoid coil 56 to a higher degree than that prevailing in the solenoid coil 54 which carries only current produced with a reduced degree of coupling between the trans formers. Coil 56 therefore moves the contact arm 50 towards the right in Figure 2. As soon as the prevalence of the influence of coil 56 over the influence of coil 54 is suificiently marked. Therefore energization of the propelling solenoid 14 ceases and the solenoid 16 is switched in.

Conversely, upon movement of the piston to the left, the secondary winding 76 of the transformer will produce an energizing current for solenoid coil 54 which enables it to draw the contact arm 50 to the left in Figure 2, thus cutting out solenoid 16 and energizing solenoid 14.

The modification shown in Figure 3 illustrates the manner in which the rather poor efiiciency of the transmission of power from the propelling solenoids to the piston reciprocating within the cylinder may be improved. As before described, a cylinder of nonmagnetic material is surrounded by coaxial propelling solenoid coils 14, 16 respectively. The cylinder is longitudinally divided into two halves or sections designated by 100 and 100a and each section or half cylinder carries a structure which permits to produce a magnetic circuit which is completely closed. For this purpose each half cylinder section is joined by means of a rectangular pole piece 102 to a core 103 surrounded by a coil 104. The pole piece 102 acts preferably and simultaneously as a lid closing the cylinder, thus transforming the cylinder section 100 and the core 103 into a U-shaped structure, both legs of which are provided with coils. The coils 14 on the leg represented by the cylinder section 100 are the propelling coils while the coils 104 are reinforcing the magnetic flux through the structure and are connected in parallel with the propelling coils. They are energized simultaneously with said coils. On the other side of the core 103 a bar or plate of rectangular shape 105 provided with a central opening 106 is used, the opening fitting exactly over the cylinder 10. One half of said bar 105 therefore closes the magnetic circuit of one cylinder section 100 while the other half performs a similar function for, the U- shaped structure connected with the other section 100a of the cylinder 10. This section is constructed in the same way and is provided with a pole piece 112 forming a cylinder lid of ferro-magnetic material and with a core 113 surrounded by a coil 116 connected in parallel to coil 16.

As indicated in dotted lines and by means of arrows energization of coils 14 and 104 produces a closed magnetic circuit passing through the piston 12 whenever the piston is within the cylinder section 100 and through the core 103 and the two pole pieces 102 and 105. As no open circuit or gap is passed by the magnetic flux the magnetic force is used in a much more eflicient and economic way and the core 12 moves therefore in a highly concentrated field.

As will be seen from the figure the delivery and supply opening 121 and 122 are in this case not arranged in the lids, but are set back from the lids so that they are overrun by the piston proceeding into its end position and are closed by the piston when in this position. Therefore a fluid column will remain in the cylinder when the piston 12 moves towards its end position which fluid column acts as a cushion for the piston. This method therefore produces a smoother running of the piston within the cylinder.

The switching relays or solenoids 54, 56 operating the switch arm 50 are the same as described before, but their energization is in this case produced by means of induction coils 108, 110 which are seated on the ends of the cylinder and which are coaxial with the cylinder. These coils may be used directly as a source of an inductive current to be transmitted to the switching solenoid. While no current flows in the coil 110 for instance, as long as piston 12 does not reach the end of its stroke, it will be clear that when piston 12 enters the space surrounded by coil 110 or 108 a strong inductive current will be produced, as piston 12 while in the magnetic circuit indicated in dotted lines, is to be considered as a strong magnet producing an induction current in the coil. This induction coil may be strong enough to operate switching relay 54 or 56 without the assistance of any external source of current.

The same arrangement may also be used if A. C. solenoids are employed in which case the piston 12 acts as a core coupling the solenoid coils 16 or 14 with the induction coils 110, 108 respectively.

It may be mentioned in this connection that the specific construction of the cylinder and of the added cores 103 and 113 may be used in connection with any one of the modifications shown in the other figures in order to improve the efficiency of the transmission. It will also be clear that this construction according to which one section of the cylinder is transformed into a U- shaped frame is not in any way connected with the means for producing currents or current differences in the control circuits.

The modification shown in Figure 4 illustrates a further control means for shifting the connections of the source of current from one propelling solenoid to the other at the end of the stroke of the piston. The basic arrangement is the same as that described in connection with Figure 1 and need not be described again. An armature 115 extends along the cylinder from one end to the other and is arranged to rock around a fixed pivot 116 suitably held at a small distance from but in proximity to the cylinder 10. Preferably the pivot 116 is arranged in the plane of symmetry bisecting the cylinder 10. The armature consists of a longitudinally extending member carrying at its ends two pole pieces 120, 124 projecting towards the axis of the cylinder and having their ends arranged in front of the central portion of the cylinder ends. These pole pieces are therefore substantially at right angles to the longitudinal member.

The armature consists of ferro-magnetic material and its pole pieces are so arranged that when the armature is in its central or middle position the pole pieces are both at substantially equal distance from the cylinder ends and are parallel to the same. When one of the pole pieces is attracted it moves towards the cylinder while the other pole piece in this case moves away from the cylinder ends.

The armature 115 is pivoted by means of the arm 117 to the pivot 116, the arm being moreover provided with a lever or rod 118 carrying a pin 119 entering a slot 131 on the frame 128 of a tiltable mercury switch which is adapted to pivot around a fulcrum 129, thus changing the position of the mercury switch with respect to the horizontal when the rod 118 is moved in the one or other direction.

The mercury switch 125 has a pair of contacts at each end which contacts are bridged by the mercury filling.

The contacts at one end are connected with the leads 126 and 127 the former lead being connected with conductor 44 leading to the source of current 42, while lead 127 is connected with solenoid 16. The contacts of the mercury switch on the other side are also connected with lead 126 connected with the battery and with conductor leading to solenoid 14.

When the piston reciprocates and moves toward the left in Figure 4, for instance, the pole piece 120 is attracted as the piston concentrating the magnetic lines of force acts as a magnet, and moves toward the cylinder end as far as it can. Thereby the armature 115 is rocked and adopts an inclined position pulling the lever 118 upwardly in Figure 4. This lifts the frame 128 carrying the mercury switch and brings the mercury switch into a tilted position as shown in the figure in which the contacts at the right end of the mercury switch in the figure are bridged by the mercury filling thus connecting the solenoid 14 with the battery lead 44 by means of conductor 130. Solenoid 14 is thereby energized as it is now connected with the source of current and attracts the piston 12 which moves toward the right end of the cylinder in Figure 4. When this movement has proceeded so far that the piston nears the end, the magnetic at traction of the piston acts on the armature pole piece 124 which is attracted so that the armature 115 is tilted counter-clockwise with the arm 118 now moving downwardly in the figure. The mercury switch now adopts the position in which the left contact pair is bridged by the mercury filling, as the frame 128 moves down with 7 rod 118. Thereby the lead 127 is now connected with the battery connection 44 and the left solenoid in the figure is energized.

in order to improve the eii'iciency'of thisarrangement the armaturemay-be provided with bosses 140, 141 acting as auxiliary pole p1eces, through which the magnetic circuit, generated by the propelling solenoid coil which is active at one time and which passes through the piston, may be closed, as shown in l'igure 5. The cylinder 10 in this case is preferably provided with t'erromagnetic collars 170, 171 which are shrunk or otherwise fixed on the cylinder 10 on both sides of and in close proximity to the plane of symmetry, bisecting the cylinder 10 longitudinally.

Whenthe piston is on the'left side in Figure for instance, the magnetic circuit may be closed through piston 12, pole piece 120, armature 115, auxiliary pole piece or boss 140 and collar 170 through which the magnetic flux returns to the other end of the piston 12. While there are several gaps in this circuit the circuit can nevertheless be considered as a closed one and therefore the eificiency of the magnetic action is substantially improved.

A further modification of the invention, increasing the efiiciency of the electromagnetic propelling mechanism, is shown in Figure 6. According to this modification the piston 12 is provided with two projecting plungers 155, 156 each working within a small cylinder 150, 152 re spectively. The cylinders are provided with a supply and delivery opening 153, 154 connected with the supply and delivery pipes 24. These cylinders may be made of steel preferably provided with a brass lining 158, 159.

The piston in this case is preferably surrounded by a non-magnetic cylinder 160 which in its turn may be surrounded by the propelling solenoid coils 14, 16. A ferro-magnetic casing 162 may in this case be arranged surrounding the propelling solenoid coils 14, 16.

It will be noted that the small. cylinders 158, 159 are sealed by the pistons 155, 156 but that no special sealing means forthe pistons are required because they are merely in communication with'the interior of the closed cylinder 160. Thefluid within the said cylinder circulates freely through openings 165 when the piston reciprocates. This arrangement therefore provides means for producing relatively large fluid pressures.

The control of the current supply to-the solenoids 14, 16 is again effected by meansof induction coils 108, 110, switch relays 54, 56, and a switch lever 50 as described in connection with Figure 3.

Obviously the'piston may now work within a closed magnetic circuit which is always closed through the casing 162 and the plungers 155, 156. In this way .a higher efficiency of the operation and especially of the magnetic propelling action may be obtained, the piston in this case being mainly a propelling means carrying the fluid displacing plungers.

Obviously a number of further modifications may be made and those shown in the various figures may be combined. it willmoreover be clear that changesof an unessential nature may be made without in any way departing from the scope of the invention as defined in the annexed claims.

' Having described the invention, what is-clairned as; new 1s:

1. A device for reciprocating a ferro-magnetic piston within a pump cylinder, provided with a plurality of propelling coils, alternatively energized from a source of direct currents and controlled by an electromagnetic propulsion control switch, closing and opening the energizing circuits of said propelling solenoids, comprising a reactance coil connected with a source of alternating currents and with a reactance circuit, an operating coil operating the propulsion control switch, said reactance coil being located near the end of the pump cylinder, and coaxial with the cylinder, the alternating electromagnetic field of the reactance coil intersecting the cylinder end into which the ferro-magnetic piston moves during reciprocation at the end of its stroke, the ferromagnetic piston upon approachzto or uponreceding from the cylinder end producing variations of the inductance of the reactance coil which, in their turn, produce varia tions in the reactance of the reactance circuit, and the reactance changes producing current fluctuations acting on the operatlng coils of the propulsion control switch, the change of the inductance of the reactance coil due to the movement of the i'erro-magnetic piston thus operating the said propulsion control switch.

2. 1n the device as claimed in claim '1, wherein a reactance coil is arranged near each end of the cylinder and two operating coils are inserted into reactance circuits connected with said two reactance .coils, said two operating coils being arranged for common differential operation of a switch arm, the movement of the piston within the cylinder towards one end producing-simultaneously an increase of the reactance in a reactance circuit connected with the reactance coil at one cylinder end and a decrease of the reactance in a reactance circuit connected with the reactance coil at the other end, and thereby opposite current fluctuations in the operating coils, resulting in a control movement of the switch arm c0ntrolling the energization of the propelling coils.

3. A device for reciprocating a retro-magnetic piston within a pump cylinder, provided with propelling coils, alternatively energized and deenergized by energizing circuits including a source of direct current, the energization and deenergization of the propelling coils being controlled by a propulsion control switch, comprising operating solenoids controlling the propulsion control switch, variable reactance coils, one at each end of the pump cylinder and coaxial with said cylinder, connected with a reactance circuit, including a source of substantially constant alternating currents, the reactance of said last-named circuit varying with changes of inductance in the reactance coils, produced by the t'erro-rnagnetic piston, when reaching the end of its stroke and intersecting the alternating electromagnetic field of a reactance coil, the operating solenoids of the propulsion control switch being controlled switch being controlled by the current fluctuations produced by the variations of the reactance in the reactance circuit, entailed by the change of the inductance of the reactance coil when the alternating electromagnetic field of the reactance coil is influenced by the ferro-magnetic piston when the latter reaches the end of its stroke within the cylinder, the operation of the solenoids of the propulsion control switch producing thel encrgization and deenergization of the propelling cor s.

4. The device as claimed in claim 3, wherein the reactance coils are connected in parallel reactance circuit branches, with the source of alternating currents arranged in a branch commonto said parallel branches, each one of the operating solenoids of the propulsion control switch being connected with one of said parallel reactance circuit branches in series with the variable reactance coils.

5. The device as claimed in claim 3, wherein each reactance coil forms a primary of a transformer with two inductively coupled transformer coils, the two reactance coils at the two ends of the cylinder being connected with a circuit including a source of alternating current, while each of the secondary coils of the transformer is connected with an energizing circuit containing one of the operating solenoids of the propulsion control switch, the transformer coils of each transformer being coupled by means of an iron core coaxial with and axially aligned with the axis of the cylinder at each end thereof.

References Cited in the file of this patent UNITED STATES PATENTS 494,956 Johnson et a1 Apr. 4, 1893 496,331 Van Depoele Apr. 25, 1893 581,204 Heftye Apr. 20, 1897 1,637,425 Nagel Aug. 2, 1927 1,640,742 Wallace et al. Aug. 30, 1927 1,647,147 Roller Nov. 1, 1927 1,804,376 Cobe May 5, 1931 1,974,262 Cobe Sept. 18, 1934 2,365,632 Fisher Dec. 19, 1944 

